1. Field of the Invention
The invention relates generally to devices for treating femoral fractures and, more particularly, to intramedullary rods and nails.
2. General Background
There are a variety of devices used to treat femoral fractures. Subtrochanteric and femoral shaft fractures have been treated with the help of intramedullary nails which are inserted into the marrow canal of the femur to immobilize the femur parts involved in fractures. An angled cross-nail or locking screw is inserted through the femur and the proximal end of the intramedullary rod. In some varieties, one or two screws may also be inserted through the femoral shaft and through the distal end of the intramedullary nail. The standard intramedullary nails have been successfully employed in treating fractures in lower portion of the femoral shaft.
Fractures of the neck, head or trochanters of the femur have been successfully treated with a variety of compression screw assemblies which include generally a compression plate having a barrel member, a lag screw and a compressing screw. The compression plate is secured to the exterior of the femur and the barrel member is inserted into a predrilled hole in the direction of the femoral head. The lag screw which has a threaded end and a smooth portion is inserted through the barrel member so that it extends across the break and into the femoral head. The threaded portion engages the femoral head. The compressing screw connects the lag screw to the plate. By adjusting the tension of the compressing screw the compression (reduction) of the fracture can be adjusted. The smooth portion of the lag screw must be free to slide through the barrel member to permit the adjustment of the compression screw. A number of patents to Brumfield, and the assignee of this application relate to intramedullary nail prothesis with transverse and diagonally extending bone screws including U.S. Pat. Nos. 4,827,917, 5,167,663, and 5,312,406.
The Russell-Taylor interlocking nail system manufactured by Smith and Nephew Richards, Inc. of Memphis, Tenn. includes an intramedullary rod having two pairs of holes through its proximal end. The axes of the pairs of holes intersect to provide a left or right orientation for insertion of a single locking screw. The screw is designed to pass from the greater to the lesser trochanter. There is not sufficient mechanical support to allow usage of the locking screw in the direction towards the femoral head because the second pair of holes weaken the nail when loaded in that direction. Further, the locking screw is a fully threaded screw which does not permit sliding of the screw relative to the intramedullary rod.
Compression screw assemblies are shown by the following patents: Fixel U.S. Pat. No. 4,432,358; Callender, Jr. U.S. Pat. No. 3,374,786; Pugh et al. U.S. Pat. No. 2,702,543; Griggs U.S. Pat. No. 4,530,355; Blosser, U.S. Pat. No. 3,094,120; and Wagner U.S. Pat. No. 3,842,825. The Blosser and Wagner patents illustrate the use of multiple screws to prevent rotation of the lag screw relative to the compression plate and barrel member. A surgical bone pin which functions like a lag screw and compressing screw but which does not include a compression plate is known by Cochran et al. U.S. Pat. No. 3,103,926.
A British patent GB 2,167,775A discloses an intramedullary nail for setting broken long bones. The nail has a head, a shank and a tip portion provided with an open ended groove for engaging a bolt previously inserted into the bone transverse to the bone axis to secure the nail to the bone. The Mareno patent 4,733,654 discloses an intramedullary nailing assembly that is adapted to the internal fixation of comminuted femoral fractures, which combines a conventional femoral nail, and extension and a set of pins interlocked with the nail and its extension. The extension is designed to be inserted into the proximal end of the femoral nail, and is predrilled to accept pins, some of which extend obliquely onto the femoral neck. A drill guide which can be inserted in the proximal end of the extension provides a convenient tool for predrilling the femur at the proper places and at the proper angles. The nail itself can be predrilled to receive pins on a bench mounted drilling guide.
The Chapman patent discloses a modular femoral fixation system for use in the treatment of femoral disorders resulting from injury, disease, or congenital defects. The apparatus includes at least three interconnectable components:
1) an elongated epiphyseal/metaphyseal implant, PA1 2) intramedullary rod, and PA1 3) an angled side plate having an elongated plate portion adapted to be secured to the outer cortical wall and a hollow sleeve adapted to extend into the femur. The epiphyseal/metaphyseal implant can be connected to either the angle side plate or the intramedullary rod. The system may also include an elongated bone plate connectable to the angle side plate, one or more additional epiphyseal/metaphyseal implants of variable length, and additional angled side plate, a distal buttress plate connectable to the elongated bone plates, and a plurality of bone screws of a universal design. Preferably, many or all of these components of the system are made of an inner, resilient titanium base alloyed.
The Grosse-Kempf nail manufactured by Howmedica Company of Rutherford, N.J. is believed to be one of the earliest intramedullary nailing devices introduced into the United States. The Grosse-Kempf nail includes a threaded hole in the intramedullary rod for receiving the interlocking screw. The fully threaded cannot slide through the threaded hole to permit the type of compression found in the compression screw assemblies discussed above. Furthermore, the axis of the threaded hole coincides with a line between the greater to lesser trochanter and not in the direction of the femoral neck.
Zickel U.S. Pat. No. 3,433,220, which issued on Mar. 18, 1969, discloses an intramedullary rod and cross-nail assembly which is useful in treating fractures occurring in the upper one-third or subtrochanteric portion of the femur. The Zickel nail is a solid intramedullary nail having a single proximal tri-flange cross-nail which is inserted in the direction of the femoral head. The intramedullary rod is curved in two planes to mimic the shape of the femur. The solid cross section does not permit insertion over a guide rod, thus preventing the use of the Zickel nail for comminuted and distal fractures of the femur because the closed surgical technique cannot be practiced. The rigid tri-flange cross-nail is not suitable for use in treating femoral neck fractures because the cross-nail must be locked into position by a set screw to prevent backing out. Adequate compression cannot be achieved. As stated above, the sliding compression screw has been found to be most effective in treating femoral neck fractures.
The commercially available Kuntscher Y-nail includes a flanged cloverleaf shaped intramedullary nail which is inserted through a hole in a single femoral neck nail. The rod includes a longitudinal slit. The Kuntscher device is indicated only for unstable trochanteric fractures. Neither the Kuntscher device, nor the Zickel nail, includes distal anchoring means and both therefore are not useful for treating distal fractures. The femoral neck nail of the Kuntscher device, which is angled toward the femoral neck is locked into place by the intramedullary rod. Thus, the Kuntscher Y-nail is also not indicated for femoral neck fractures.
A bone-nail which permits left-right orientation by means of "criss-cross" nail holes is shown by Enter U.S. Pat. No. 4,475,545.
For unstable subtrochanteric fractures, the extreme loads have frequently caused implants, such as hip compression screw plates, to fail. In cases of severe comminution of the femoral shaft, existing interlocking nails have at times not provided adequate strength.